1. Field of the Invention
The present invention relates to a method for transmitting data in a telecommunication system including at least one transmitter and one receiver, said transmitter being intended to transmit a signal formed by at least one sequence of Np pulses over Np time windows, each pulse being enclosed within a time chip whose position within its relevant time window is defined by a chip number.
So-called Ultra-Wide Band systems (further referred to as UWB systems) are currently studied with the aim of assessing their relevance for future wireless mobile communication techniques. In such a UWB system, each transmitter may be identified by a signature formed by the above-mentioned chip numbers, which signature is in itself quite sturdy and may thus be reliably and accurately communicated to all potential receivers.
The pulses used in UWB systems are very short, having for example a duration lower than 0.1 nanosecond, which offers to such systems bandwidths at least as large as 10 GigaHertz, entailing high flexibility and hence numerous possible applications for such systems.
The above-described signal may form a carrying signal on which information can be encoded by modulation of said carrying signal, for example by performing phase or amplitude modulation of one or more pulse sequences.
2. Description of the Related Art
A major problem which hinders development of such systems lies in the identification, by a receiver, of relevant information carried by incoming signals. In the present state of the art, a signal characterization is often performed by the receiver by correlating a received signal delivered at the output of a receiving antenna, which received signal may be exclusively constituted by noise or, alternatively, may include an incoming carrying signal, with a gliding model of the waveform such a carrying signal should have. Such a gliding correlation enables to obtain an exhaustive knowledge of the received signal, by performing in effect a complete mapping of this signal, which will yield all useful information related, for example, to the phase or to the amplitude of this signal.
Unfortunately, this gliding correlation technique is not realistically applicable as such to the characterization of sequences of Np pulses lasting less than 0.1 ns each and enclosed in time windows having each a width of roughly 100 ns. In such an example, with for example Np=128 and a sampling interval of 10 ps, the scanning of the whole duration of a pulse sequence would require 1.28.106 successive pulse sequences for its completion and would then last 16 seconds, which is not acceptable.
It should also be noted that, during the considerable time required for performing the characterization of a pulse sequence according to the gliding correlation technique described above, communication conditions between the transmitter and the receiver may change, i.e. a communication channel between these devices may be altered, for example due to movements of one or both devices, in the course of a single signal characterization step, with adverse effects on the accuracy of the results yielded by said signal characterization step. The signal carrying the pulse sequences may even disappear before its characterization is completed.